High speed imaging apparatus for CCD based scanners

ABSTRACT

A high speed imaging apparatus for CCD based scanners comprises a housing having separate compartments which complement modular assemblies installed therein. A decoder compartment houses components associated with locating and decoding an image. An optics compartment houses the mirrors and associated optics for reflecting the subject image onto the CCD detector. A lighting compartment includes high intensity lamps and the associated components for illuminating an object to be imaged. The lighting compartment includes a heat management system which removes the heat from the high intensity lamps and prevents heat from migrating to other compartments within the housing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to an apparatus for illuminatingcoded information symbols. More particularly, the present inventionrelates to a high speed imaging apparatus for CCD based scanners.

2. Description of Prior Art

There are many difficulties associated with imaging objects or bar codesymbols and other machine readable symbologies on packaging. Erroneousimaging of a human or machine readable symbology may be the result ofpoor printing of the symbology on a label or extraneous markings orcontaminants located on the label. However, erroneous imaging is oftenthe results of poor lighting conditions. Proper illumination is one ofthe most important requirements for any machine imaging system.

The illumination of an object or a label is particularly critical forhigh speed scanning systems that employ CCD detectors. As is well knownby those skilled in the art, the ability of CCD scanning systems toaccurately detect an object depends upon the amount of light that isreflected from the region of interest onto the CCD detector. The amountof light detected by the CCD detector is a function of both theintegration period and the intensity of illumination.

Many current imaging systems in the material handling field includevariable speed conveyors, wherein the conveyor speed varies with thevolume of packages handled by the system. If a low intensityillumination level is selected for low speed conveyor operation, thesame illumination level may be insufficient for accurate imaging whenthe conveyor speed is increased. If a high intensity illumination levelis selected, the light may saturate the CCD detector when the conveyoris operating at low speeds.

High intensity illumination sources have also been known to generatetremendous amounts of heat, thus creating “wave distortions” which mayinhibit the ability of a CCD detector based system to accurately resolvethe image. Additionally, the high intensity sources create an annoyanceand even a safety hazard to nearby operators.

Accordingly, there exists a need for an illumination assembly whichprovides the desired illumination for operation of a conveyor at anyspeed.

SUMMARY OF THE INVENTION

The present invention is a high speed imaging apparatus used for CCDbased image acquisition systems. The apparatus comprises a housinghaving separate compartments which complement modular assembliesinstalled therein. A decoder compartment houses a CCD camera head unitand components associated with locating and detecting and decoding animage. An optics compartment houses the mirrors and associated opticsfor reflecting the image onto the CCD detector. A lighting compartmentincludes high intensity lamps and the associated components forilluminating the object to be imaged. The lighting compartment includesa heat management system which removes the heat from the high intensitylamps and prevents heat from migrating to other compartments within thehousing.

Accordingly, it is an object of the invention to provide an illuminationassembly which provides the optimum amount of illumination according tothe demands placed upon the system.

It is a further object of the invention to provide a high speed imagingapparatus with an effective heat management system.

Other objects and advantages will become apparent to those skilled inthe art after reading the detailed description of a presently preferredembodiment.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of the high speed imaging apparatus of thepresent invention;

FIG. 2 is a perspective view of the modular illumination assembly of thepresent invention;

FIG. 3A is a side view of the lighting assembly of FIG. 2;

FIG. 3B is a perspective view of the lighting assembly of FIG. 2;

FIG. 4 is a perspective view of a plurality of modular illuminationassemblies located in parallel;

FIG. 5 is a graphical representation of the illumination profile of aprior art lighting unit;

FIG. 6 is a plan view of the window of the lighting assembly includingan aperture;

FIG. 7 is a graphical representation of the illumination profile of thelighting assembly of the present invention;

FIG. 8 is a block diagram of the illumination intensity control systemof the present invention;

FIG. 9 is a perspective view of the present invention showing theresolution of the scanning system; and

FIG. 10 is the square wave output signal from the tachometer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment will be described with reference to the drawingfigures where identical numerals represent the same element throughout.A high speed imaging apparatus 12 in accordance with the presentinvention is shown in FIG. 1. The imaging apparatus 12 comprises a frame14 which supports a main housing 16 above a conveyor 18. As packages 20travel along the conveyor 18, they pass under the housing 16. Thepackages 20 are illuminated to facilitate the detection of the packages20 and any human or machine readable symbologies located thereon, suchas a bar code 22. For simplicity, the invention will be described withreference to the detection and decoding of bar codes. However, thepresent invention is applicable to any type of system for imagingobjects or imaging human and machine readable symbologies.

There are many factors which can affect the ability of the apparatus 12to accurately detect each bar code label 22; including the speed of theconveyor 18, the illumination intensity, and the ability of theapparatus 12 to accurately focus on the subject bar code label 22. Thesefactors are considered by the imaging apparatus 12 of the presentinvention in illuminating and detecting bar code symbols.

Referring to FIG. 2, the imaging apparatus 12 made in accordance withthe teachings of the present invention is shown. The apparatus 12includes a lighting assembly 40 and a main housing 42. The main housing42 comprises three separate compartments: 1) an optics compartment 44;2) a decoder compartment 46; and, 3) a lighting compartment 43. Accesshatches 57, 59, 61 are also provided for easy access to componentswithin each compartment 43, 44, 46.

The optics compartment 44 houses the mirrors and associated optics forreflecting an image of the subject bar code label 22 onto a CCDdetector. The decoder compartment 46 houses the components, such as aCCD camera head unit and the image processing architecture which is usedfor detecting and decoding the bar code image. The decoder compartment46 may be configured to house different types of CCD detectors from anymanufacturer.

The lighting compartment 43 compliments the lighting assembly 40 forsecuring the lighting assembly 40 to the main housing 42. Referring toFIG. 3A, the lighting assembly 40 includes a combinationreflector/heatsink 50, a window 51, a cross-flow blower 52, lamp sockets56, lamps 58 and an electronics compartment 60. The lamps 58 provide thesource of illumination 62 for bar code detection. The lamp sockets 56secure the lamps 58 in place and provide electrical power to the lamps58. Preferably, there are two lamps 58 and each lamp 58 is of the 400watt high pressure sodium type.

In order to utilize as much of the output from the lamps 58 as possible,a combination reflector/heatsink 50 is utilized. The combinationreflector/heatsink 50 is an aluminum extrusion which is polished to areflective mirrored surface 70 on one side and includes heatsink fins 72on the other side. The combination reflector/heatsink 50 provides asimple and inexpensive means for both light reflection and heat removal.With respect to light reflection, illumination emitted from the lamps 58in a direction away from the conveyor 18, will be redirected by thereflector/heatsink 50 through the window 51 and toward the conveyor 18.

The plurality of heatsink fins 72 provide structural rigidity to thereflector/heatsink 50. Thus, the reflector/heatsink 50 will notsubstantially deform even in harsh environmental conditions. This is asignificant advantage over prior art reflectors which typically comprisethin reflective materials supported by a frame or other structure. Theseprior art reflector assemblies can be easily dented or deformed, thuspermitting light to be misdirected.

With respect to heat removal, since the reflector 50 is also a heatsink50, heat removal is extremely efficient. Heat removal is furthereffected by a laminar air flow 75 across the heatsink fins 72. Thecross-flow blower 52 draws air through the cool air intake plenum 71from underneath the lighting assembly 40 and across the heatsink fins72. The heated air is discharged out the back of the lighting assembly40 through a warm air exhaust plenum 73. The laminar air flow 75 coolsthe back and top of the reflector/heatsink 50. The laminar air flow 75also prevents the build-up of heat in the lighting assembly 40 whichwould eventually migrate to the optics compartment 44 and create opticaldistortions due to heatwaves or an “oasis effect”.

The cross-flow blower 52 is effective not only in cooling thecombination reflector/heatsink 50, but also in directing the hot airaway from adjacent bar code scanners 61, 63. Accordingly, severallighting assemblies may be placed in parallel for a wide conveyor system59 as shown in FIG. 4.

Referring to FIG. 3B, the lighting assembly 40 is shown in greaterdetail. The laminar air flow 75 thermally isolates thereflector/heatsink 50 from other portions of the lighting assembly 40.This effectively prevents thermal degradation of components in theelectronics compartment 60 which are more susceptible to damage fromheat related stress. A fan 54 removes any remaining heat from theelectronics compartment 60.

It should be appreciated by those of skill in the art that not all ofthe heat generated by the lamps 58 will be removed by the laminar airflow. Cooling of the reflector/heatsink 50 is further enhanced by directsuspension of the reflector/heatsink 50 at the side walls 78 of thelighting assembly 40. This permits the remaining heat to be radiated outalong the heat fins 72 and onto the side walls 78.

In order to monitor the intensity of the lamps 58, a light intensityfeedback system 80 is employed. The system 80 comprises a light pipe 82,83, for each lamp 58 which conducts a portion of the illumination fromeach lamp 58 to a photo sensitive device such as a photo resistor 65, 67which is located in the electronics compartment 60 of the lightingassembly 46. The light pipes 82, 83 are thermally conductive tubes whichare selectively placed within the same laminar air flow 75 that coolsthe reflector/heatsink 50. Each photo resistor 65, 67 monitors theillumination transmitted by its respective light pipe 82, 83 andprovides an electrical output corresponding to the relative illuminationintensity for that lamp 58. This provides a feedback arrangement wherebythe illumination of each lamp 58 may be individually monitored andcontrolled, as will be described in greater detail hereinafter. The useof the conductive light pipes 82, 83 permits the photo resistors 65, 67to directly monitor the relative intensity of the lamps 58 whileminimizing the undesired effects of heat related degradation which wouldbe caused by locating the photo resistors 65, 67 in close proximity tothe lamps 58.

The modular design of the present invention provides significantadvantages over prior art systems. Since the main housing 42 providesthree separate compartments, (the optics compartment 44, the decodingcompartment 46 and the lighting compartment 43), components within eachcompartment 43, 44, 46 may be removed without disturbing components inother compartments. The modular design of the lighting assembly 40provides for quick removal and replacement. Additionally, thecompartmentalization of the main housing 42 provides distinct thermalseparation between compartments 43, 44, 46 thus minimizing any adverseeffects upon electrical components from heat generated by the lamps 58.

One of the common problems associated with prior art lighting units isthat the illumination emitted by these lighting units has an unevenprofile as shown in FIG. 5. The illumination intensity tends to begreater near the middle of the profile and tapers off at the ends of theprofile, which typically coincides with the outer edges of the conveyor18.

Referring to FIG. 6 the lighting assembly 40 of the present inventionemploys an aperture for equalizing the illumination intensity across thewidth of the illumination profile. The aperture 47 reduces the intensityof the illumination at the center of the illumination profile, but doesnot substantively affect the illumination at either end of theillumination profile. Accordingly, a more even illumination profile asshown in FIG. 7 is achieved. An even illumination profile increases theperformance of the imaging apparatus 12 by permitting the acquisition ofhigher quality, more uniform CCD images. As would be appreciated bythose of skill in the art, the shape of the aperture 47 may be modifiedto achieve a different illumination profile, depending upon the profiledesired for a specific application.

The ability to individually control the intensity of the lamps 58 isalso critical in assuring proper operation of the CCD detector.Referring to FIG. 8, a microprocessor 100 is used to determine anintensity value based on certain operating conditions. Using a lookuptable, the microprocessor 100 outputs an analog level corresponding to adigital word to a lamp driver 103. The analog level represents thedesired illumination intensity. The lamp driver 103 drives the lamps 58accordingly. Preferably, each lamp 58 is individually monitored andadjusted to the desired intensity. This permits the lighting assembly 40to account for fluctuations in the performance of each lamp 58, whichcan vary greatly as the age of the lamps 58 increase.

The intensity of the lamps 58 may be controlled in response to severaldifferent parameters. In the present invention, the intensity of thelamps 58 is controlled in relation to: 1) the speed of the conveyor 18;and 2) the height of each package being scanned. With respect to thespeed of the conveyor 18, with a fixed resolution CCD system, a line ofdata is acquired for a fixed distance of conveyor 18 travel. The timerequired to travel the distance varies with the speed of the conveyor18. Accordingly, the exposure time for a line of data is equal to thetime required to travel the fixed distance. At slower conveyor 18speeds, the exposure time is longer than at higher conveyor 18 speeds.Accordingly, a lower illumination intensity is required for longerexposure times.

A conveyor 18 tachometer 110 outputs a signal to the microprocessor 100,which determines the desired intensity value for that particularconveyor speed. The microprocessor 100 outputs an analog level to thelamp driver 103 and the intensity of the lamps 58 is adjustedaccordingly. At slower conveyor 18 speeds, a lower illumination level isdesired. This results in lower power consumption and increased operatorcomfort level.

The intensity of the lamps 58 may also be controlled in relation to theheight of each package being scanned. For packages which are shorter,and thus further away from the scanner, a higher illumination intensityis required to keep a constant signal-to-noise ratio in the CCD detectedimages. For taller packages which are closer to the scanner, a lowerillumination intensity is required. The package height detector 111 maycomprise a light curtain, as shown in FIG. 1, or any other type ofconventional height detecting means. The height detector 111 determinesthe height of a package and forwards this information to themicroprocessor 100. The microprocessor 100 determines the desiredintensity value for that particular package height. As would beappreciated by those skilled in the art, package height and conveyorspeed may be simultaneously considered to calculate an optimum lightingintensity.

In another aspect of the invention, tachometer resealing is used todirectly control the CCD line rate, (or resolution), of the imagingapparatus 12 along the direction of travel. As shown in FIG. 9, theresolution of the imaging apparatus 12 across the width of the conveyor18 varies with the distance of an object from the imaging apparatus 12.Imaging inaccuracies may result if this variation in the resolution isnot taken into consideration by the imaging apparatus 12 while imaging abar code located on the package. This is particularly critical inapplications where time delayed integration (TDI) CCD detectors areused, since the shifting of the charge must be closely coupled withobject motion to maintain accurate image resolution.

An example of the variation in scanning resolution is shown in FIG. 9.The imaging apparatus 12 may scan packages at a plurality of heights200, 202, 204. The tachometer 110 produces an output signal which isproportional to the speed of the conveyor 18. One pulse is generated forevery 0.01 inches of conveyor travel, which is designated the “y”direction. Thus, the resolution of the imaging apparatus 12 is constantin the Y direction. At height 200 the field of view X₁ of CCD detectorwill be relatively small in the X direction. This results in highresolution in the X direction. At height 202, the field of view X₂ islarger than the field of view X₁ at height 200. However, since the samenumber of pixels on the CCD detector image the wider field of view X₂,the resolution in the X direction has decreased. At this height 202, theresolution in the X direction is equal to the resolution in the Ydirection Y₂. At height 204 the field of view X₃ has again increased,thereby decreasing the resolution in the X direction. Accordingly, theresolution in the X direction at height 204 will be less than theresolution in the Y direction. This variation of resolution in the Xdirection due to package height causes imaging anomalies and decodinginaccuracies.

Referring to FIG. 10, the signal that tachometer 110 produces is a 50%duty cycle square wave 120 which is output to the microprocessor 100.The microprocessor 100 digitally samples the square wave 120 and a rawdigital count corresponding to the time between rising edges 122 isobtained. Using a lookup table, the microprocessor 100 obtains a scalingfactor, which is a function of the lens focal length and objectdistance. The microprocessor 100 applies this scaling factor to the rawdigital count and generates a rescaled digital count. The rescaleddigital count provides the CCD line clock signal, which is output to theCCD detector. Accordingly, the CCD line clock rate is modified tomaintain a 1:1 magnification ratio in both the X and Y directions. Forexample, if a package is tall, and thus close to the imaging apparatus12, the CCD line clock rate must be increased. The microprocessor 100obtains the raw digital count and accesses the lookup table for ascaling factor. At this height, the scaling factor may be on the orderof ten per-cent. The raw digital count is multiplied by 1.1 to providean increased CCD line clock signal. Implementation of the resealingmethod as described will provide greatly improved performance of TDIbased CCD detectors in large depth of field applications.

Although the invention has been described in part by making detailedreference to the preferred embodiment, such detail is intended to beinstructive rather than restrictive. It will be appreciated by thoseskilled in the art that many variations may be made in the structure andmode of operation without departing from the spirit and scope of theinvention as disclosed in the teachings herein.

What is claimed is:
 1. An apparatus for imaging an object within apredetermined region comprising: means for illuminating the regioncomprising: means for producing light; reflector means for directingsaid light toward said region; and said reflector means including meansintegral with said reflector means for removing heat generated by saidlight producing means; detecting means for receiving reflected lightfrom said object when disposed within the region; means for focusingreflected light onto said detecting means; and means for monitoring theintensity of said light producing means comprising a photo sensitiveelement and means for transmitting light from said light producing meansto said element.
 2. The apparatus of claim 1 wherein said transmittingmeans comprises a thermally conductive tube for thermally insulatingsaid element from said light producing means.
 3. An apparatus forimaging an object within a predetermined region comprising: means forilluminating the region comprising: means for producing light; reflectormeans for directing said light toward said region, said reflector meansincluding means integral with said reflector means for removing heatgenerated by said light producing means; detecting means for receivingreflected light from said object when disposed within the region, saidlight detecting means comprising a CCD camera head unit having a CCDdetector and an image processor; and means for focusing reflected lightonto said detecting means.
 4. The apparatus of claim 3 furthercomprising: a conveyor, for moving objects past said light detectingmeans; and means for rescaling the line clock of the CCD detectorcomprising: means for measuring the speed of said conveyor; means fordetermining the distance between the object and said light detectingmeans; and means for calculating a new line clock rate based upon saidspeed and said distance.
 5. An apparatus for imaging an object within apredetermined region comprising: means for illuminating the regioncomprising: means for producing light; reflector means for directingsaid light toward said region, said reflector means including meansintegral with said reflector means for removing heat generated by saidlight producing means; detecting means for receiving reflected lightfrom said object when disposed within the region; means for focusingreflected light onto said detecting means; means for determining thedistance between the object and said light detecting means; and meansfor modulating the intensity of said light producing means, saidmodulating means being responsive to said distance.
 6. The apparatus ofclaim 5 wherein said modulating means increases the intensity of saidlight producing means as said distance increases and decreases theintensity of said light producing means as said distance decreases. 7.The apparatus of claim 6 further including means for determining thespeed of the object relative to said light detecting means, saidmodulating means being further responsive to said speed.
 8. Theapparatus of claim 7 wherein said modulating means increases theintensity of said light producing means as said speed increases anddecreases the intensity of said light producing means as said speeddecreases.
 9. An apparatus for imaging an object within a predeterminedregion comprising: means for illuminating the region comprising: meansfor producing light; reflector means for directing said light towardsaid region said reflector means including means integral with saidreflector means for removing heat generated by said light producingmeans; detecting means for receiving reflected light from said objectwhen disposed within the region; and means for focusing reflected lightonto said detecting means; said heat removing means comprising aplurality of thermally conductive heatsink fans, and said illuminatingmeans further comprising a blower for producing a flow of air acrosssaid heatsink fins to remove heat, said flow of air being transverse tosaid heatsink fins, said light producing means, said reflector means andsaid blower being housed in a compartment separate from othercompartments of said imaging apparatus, thereby providing distinctthermal separation between said compartments.
 10. The apparatus of claim9, further comprising an electronic compartment adjacent to saidseparate compartment, the flow of air across said fins isolating andpreventing degradation of components in said electronics compartment bythe heat from said light producing means.
 11. The apparatus of claim 10comprising means for directing said flow of air so as to continueadjacent to said electronics compartment after passing across said fins.12. The apparatus of claim 11 further comprising a fan for removing heatfrom said electronics compartment.
 13. The apparatus of claim 9, whereinthe ends of the fins of the reflector means are suspended directly atthe sidewalls of the separate compartment whereby heat is radiated alongthe fins and onto the sidewalls.
 14. An apparatus for imaging an objectwithin a predetermined region comprising: means for illuminating theregion comprising: means for producing light; reflector means fordirecting said light toward said region; and said reflector meansincluding means integral with said reflector means for removing heatgenerated by said light producing means; detecting means for receivingreflected light from said object when disposed within the region; andmeans for monitoring the intensity of said light producing meanscomprising a photo sensitive element and means for transmitting lightfrom said light producing means to said element.
 15. An apparatus forimaging an object within a predetermined region comprising: means forilluminating the region comprising: means for producing light; reflectormeans for directing said light toward said region, said reflector meansincluding means integral with said reflector means for removing heatgenerated by said light producing means; and detecting means forreceiving reflected light from said object when disposed within theregion, said light detecting means comprising a CCD camera head unithaving a CCD detector.
 16. An apparatus for imaging an object within apredetermined region comprising: means for illuminating the regioncomprising: means for producing light; reflector means for directingsaid light toward said region said reflector means including meansintegral with said reflector means for removing heat generated by saidlight producing means; detecting means for receiving reflected lightfrom said object when disposed within the region; said heat removingmeans comprising a plurality of thermally conductive heatsink fins, andsaid illuminating means further comprising a blower for producing a flowof air across said heatsink fins to remove heat, said flow of air beingtransverse to said heatsink fins, said light producing means, saidreflector means and said blower being housed in a compartment separatefrom other compartments of said imaging apparatus, thereby providingdistinct thermal separation between said compartments.
 17. An apparatusfor imaging an object within a predetermined region comprising: meansfor illuminating the region comprising: means for producing light;reflector means for directing said light toward said region; and saidreflector means including means integral with said reflector means forremoving heat generated by said light producing means; detecting meansfor receiving reflected light from said object when disposed within theregion; and means for focusing reflected light onto said detectingmeans; said illuminating means further comprising aperture mean whichselectively blocks illumination from said light producing means toprovide an even illumination intensity in said region.
 18. An apparatusfor imaging moving objects comprising: means for producing an image of amoving object; means for measuring a speed of the moving object; meansfor determining a distance between the moving object and the imageproducing means; and means for rescaling along a dimension of theproduced image based on in part the measured speed and the determineddistance; and reflector means for directing light produced by a lightproducing means towards the moving object, the reflector means havingmeans integral with the reflector for removing heat generated by thelight producing means.
 19. The apparatus of claim 18 wherein therescaled dimension is a dimension associated with a direction ofmovement of the moving object.
 20. The apparatus of claim 18 wherein themoving object is on a moving conveyor belt and the speed measuring meansmeasures a speed of the moving conveyor belt to measure the speed of themoving object.
 21. The apparatus of claim 20 wherein the image producingmeans is a CCD detector and the rescaling is performed by rescaling aline clock rate of the CCD detector.
 22. The apparatus of claim 21wherein the CCD detector is a time delay integration CCD detector. 23.The apparatus of claim 20 wherein the speed measuring means comprises atachometer which produces a pulse signal proportional to the conveyorbelt speed.
 24. The apparatus of claim 20 wherein the speed measuringmeans comprises a tachometer which produces a 50% duty cycle square wavesignal proportional to the conveyor belt speed.
 25. The apparatus ofclaim 18 wherein the dimension rescaling is based on in part thedistance determination, the measured speed and a lens focal length ofthe image producing means.
 26. The apparatus of claim 25 wherein thedimension rescaling means comprises a microprocessor using a lookuptable.
 27. An apparatus for imaging moving objects comprising: a CCDdetector for producing an image of a moving object; a tachometer formeasuring a speed of the moving object; a height detector fordetermining a height of the moving object; and a processor operativelycoupled to the tachometer and height detector for rescaling a dimensionof the produced image based on in part the measured speed and thedetermined height; and wherein the apparatus having reflector means fordirecting light produced by a light producing means towards the movingobject, the reflector means having means integral with the reflectormeans for removing heat generated by the light producing means.
 28. Anapparatus for imaging moving objects within a predetermined region, theapparatus having means for illuminating the region, detecting means forreceiving reflected light from said object when disposed within theregion, and means for focusing reflected light onto the detecting means,the illuminating means having means for producing light, reflector meansincluding means integral with said reflector means for removing heatgenerated by said light producing means for directing the light towardthe region, the apparatus comprising: means for producing an image of amoving object; means for measuring a speed of the moving object; meansfor determining a distance between the moving object and the imageproducing means; and means for rescaling a dimension of the producedimage based on in part the measured speed and the determined distance.29. An apparatus for imaging moving objects in a predetermined region,the apparatus having a reflector means for directing light produced by alight producing means towards the region, the reflector means havingmeans integral with the reflector means for removing heat generated bythe light producing means, the apparatus comprising: means for producingan image of a moving object; means for measuring a speed of the movingobject; means for determining a distance between the moving object andthe image producing means; and means for rescaling along a dimension ofthe produced image based on in part the measured speed and thedetermined distance.